This application claims the priority of German patent document 197,21,217.4, filed May 21, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an arrangement for simultaneous calibration of several multi-axis gyro systems, particularly fiber-optical gyro systems, in all measuring axes by means of a single-axis rotary table.
Known fiber optic gyros which are used as rate of rotation sensors, such as disclosed, for example, in Applied Optics, Vol. 29, No. 36, Dec. 20, 1990, Pages 5360 to 5365, have measuring value sensors which generate complicated temperature-dependent output signals. The measured rate of rotation is computed from these signals, using an analyzing formula corresponding to the special gyro type. Such a computation formula is indicated, for example, in Equation 26 in the above-mentioned publication and reflects the relationship between the signals P1, P2 and P3 of the photo diodes used as measuring value sensors and the measured rate of rotation .omega.. To account for individual characteristics of the gyro, special coefficients f1 to f6 must be determined beforehand by the calibration of the gyro on a rotary table. For this purpose, the gyro is caused to rotate at several known rates of rotation; the measuring signals of the photo diodes are measured; and the coefficients are computed from them. These are then programmed into the memory of the gyro and are used from that point on as to compute inertial rates of rotation by the gyro computer.
Since the coefficients f1 to f6 depend on the temperature, in order to compensate for temperature-dependent errors, the rotations on the rotary table must be carried out at different temperatures. Therefore, to operate a gyro in the temperature range between -53.degree. C. and +85.degree. 73 C. in a temperature-compensated manner, the determination of the coefficients must take place by means of several known rates of rotation on a rotary table with an integrated temperature chamber at discrete temperature support points in the whole temperature range. The passage through the whole temperature range and the determination of the coefficients at discrete temperature support points requires considerable time, typically 12 hours.
In a three-axis gyro system, all three orthogonal axes must be calibrated individually. According to the state of the art, this can be done in two ways:
1. The coefficients are determined at different temperature support points successively, first for the X-axis, then for the Y-axis, and then for the Z-axis. The rotation about the three different axes takes place by resetting the gyro system on the rotary table to the corresponding axes at the end of the respective temperature cycle. The total time of the calibration is thus three times as long as that of a single-axis gyro, with the respective resetting times added.
2. The coefficients for the different axes can also be determined successively at the same support point temperature using a multi-axis rotary table which permits rotation about each of the axes. Thus, at a defined temperature, a rotation takes place, for example, first about the X-axis, then about the Y-axis and then about the Z-axis. In this process, the coefficients are computed for the three axes at a particular temperature; then a new support point temperature is started, and the whole operation is repeated. The time requirement for this method is comparable to that of the first method; however, in addition, a more cost-intensive multi-axis rotary table is required within the temperature chamber.
It is therefore an object of the present invention to provide an arrangement for calibrating multi-axis gyro systems, by means of which several gyro systems can be calibrated simultaneously, in a shorter time period than previously possible.
This object, and other objects and advantages, are achieved by the arrangement according to the invention, which can be used on a single-axis rotary table with an integrated temperature chamber, and the above-mentioned coefficients determined simultaneously for all measuring axes. For this purpose, each gyro system is arranged on a rotary frame in such a manner that the corresponding measuring axes of the gyro systems (that is, all X-axes, all Y-axes and all Z-axes), form an identical component of the rotation of the rotary frame and none of the components is zero. This is achieved, for example, by arranging the plane diagonals or body diagonals of the measuring axes of all gyro systems within the rotary frame at an identical angle (including the zero angle) with respect to the axis of rotation of the rotary frame. In this manner, all three measuring axes of all gyro systems are rotated simultaneously for each temperature support point and the simultaneous measuring signals of the individual photo diodes of all measuring axes are used to compute the coefficients. Subsequently, the process is repeated for the next temperature support point. This procedure thus lasts no longer than that of a single-axis gyro using a single-axis rotary table.
The rotary frame is advantageously constructed such that all gyro systems placed in it are arranged n-radiated symmetrically about its axis of rotation in a distributed manner. In addition, the gyro systems can be arranged within the rotary frame in several planes perpendicular to its axis of rotation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.